Most solid-state electronic sensors operate well for a mean luminance level. They can also operate at low luminance level, by greatly increasing the duration of integration, to the detriment of the rate of provision of images. Moreover, increasing the duration of integration may be incompatible with the application. For example a surveillance camera must typically provide 30 images per second, thus limiting the duration of integration. These sensors can also operate when the luminance level increases but beyond a certain luminance they saturate.
Certain sensors have been specially designed to operate at low luminance level. But they are very rapidly saturated even for a mean luminance when some points of the scene are brighter. These sensors include amongst them electron multiplication sensors.
Other sensors have been designed to operate at high luminance level, with complex systems making it possible to establish a light-dependent logarithmic (or at least with two slopes) response curve. These sensors cannot operate well at low luminance level.
A need exists for sensors with very high upward and downward dynamic range, that is to say sensors capable of operating both at very high luminance level and at very low luminance level, even within one and the same greatly contrasted image.